The present invention relates generally to the detection of Mycobacterium tuberculosis infection. The invention is more particularly related to polypeptides comprising a Mycobacterium tuberculosis antigen, or a portion or other variant thereof, and the use of such polypeptides for the serodiagnosis of Mycobacterium tuberculosis infection.
Tuberculosis is a chronic, infectious disease, that is generally caused by infection with Mycobacterium tuberculosis. It is a major disease in developing countries, as well as an increasing problem in developed areas of the world, with about 8 million new cases and 3 million deaths each year. Although the infection may be asymptomatic for a considerable period of time, the disease is most commonly manifested as an acute inflammation of the lungs, resulting in fever and a nonproductive cough. If left untreated, serious complications and death typically result.
Although tuberculosis can generally be controlled using extended antibiotic therapy, such treatment is not sufficient to prevent the spread of the disease. Infected individuals may be asymptomatic, but contagious, for some time. In addition, although compliance with the treatment regimen is critical, patient behavior is difficult to monitor. Some patients do not complete the course of treatment, which can lead to ineffective treatment and the development of drug resistance.
Inhibiting the spread of tuberculosis will require effective vaccination and accurate, early diagnosis of the disease. Currently, vaccination with live bacteria is the most efficient method for inducing protective immunity. The most common Mycobacterium for this purpose is Bacillus Calmette-Guerin (BCG), an avirulent strain of Mycobacterium bovis. However, the safety and efficacy of BCG is a source of controversy and some countries, such as the United States, do not vaccinate the general public. Diagnosis is commonly achieved using a skin test, which involves intradermal exposure to tuberculin PPD (protein-purified derivative). Antigen-specific T cell responses result in measurable incubation at the injection site by 48-72 hours after injection, which indicates exposure to Mycobacterial antigens. Sensitivity and specificity have, however, been a problem with this test, and individuals vaccinated with BCG cannot be distinguished from infected individuals.
While macrophages have been shown to act as the principal effectors of M. tuberculosis immunity, T cells are the predominant inducers of such immunity. The essential role of T cells in protection against M. tuberculosis infection is illustrated by the frequent occurrence of M. tuberculosis in AIDS patients, due to the depletion of CD4 T cells associated with human immunodeficiency virus (HIV) infection. Mycobacterium-reactive CD4 T cells have been shown to be potent producers of gamma-interferon (IFN-xcex3), which, in turn, has been shown to trigger the anti-mycobacterial effects of macrophages in mice. While the role of IFN-xcex3 in humans is less clear, studies have shown that 1,25-dihydroxy-vitamin D3, either alone or in combination with IFN-xcex3 or tumor necrosis factor-alpha, activates human macrophages to inhibit M. tuberculosis infection. Furthermore, it is known that IFN-xcex3 stimulates human macrophages to make 1,25-dihydroxy-vitamin D3. Similarly, IL-12 has been shown to play a role in stimulating resistance to M. tuberculosis infection. For a review of the immunology of M. tuberculosis infection see Chan and Kaufmann, in Tuberculosis: Pathogenesis, Protection and Control, Bloom (ed.), ASM Press, Washington, D.C., 1994.
Accordingly, there is a need in the art for improved diagnostic methods for detecting tuberculosis. The present invention fulfills this need and further provides other related advantages.
Briefly stated, the present invention provides compositions and methods for diagnosing tuberculosis.
In one embodiment, polypeptides are provided that comprise an antigenic portion of a M. tuberculosis antigen, or a variant of such an antigen that differs only in conservative substitutions and/or modifications, wherein the antigen comprises an amino acid sequence encoded by a DNA sequence selected from the group consisting of the sequences recited in SEQ ID NO: 1, 11, 12, 83, 103-108, 125, 127, 129-137, 139 and 140, the complements of said sequences, and DNA sequences that hybridize to a sequence recited in SEQ ID NO: 1, 11, 12, 83, 103-108, 125, 127, 129-137, 139 and 140, or a complement thereof, under moderately stringent conditions. In a second embodiment, the present invention provides polypeptides comprising an immunogenic portion of a M. tuberculosis antigen having an amino acid sequence selected from the group consisting of sequences provided in SEQ ID NO: 16-33, 109, 126, 138, 141, 142 and variants thereof
In related aspects, DNA sequences encoding the above polypeptides, recombinant expression vectors comprising these DNA sequences and host cells transformed or transfected with such expression vectors are also provided.
In another aspect, the present invention provides fusion proteins comprising a first and a second inventive polypeptide or, alternatively, an inventive polypeptide and a known M. tuberculosis antigen.
In further aspects of the subject invention, methods and diagnostic kits are provided for detecting tuberculosis in a patient. The methods comprise: (a) contacting a biological sample with at least one of the above polypeptides; and (b) detecting in the sample the presence of antibodies that bind to the polypeptide or polypeptides, thereby detecting M. tuberculosis infection in the biological sample. Suitable biological samples include whole blood, sputum, serum, plasma, saliva, cerebrospinal fluid and urine. The diagnostic kits comprise one or more of the above polypeptides in combination with a detection reagent.
The present invention also provides methods for detecting M. tuberculosis infection comprising: (a) obtaining a biological sample from a patient; (b) contacting the sample with at least one oligonucleotide primer in a polymerase chain reaction, the oligonucleotide primer being specific for a DNA sequence encoding the above polypeptides; and (c) detecting in the sample a DNA sequence that amplifies in the presence of the first and second oligonucleotide primers. In one embodiment, the oligonucleotide primer comprises at least about 10 contiguous nucleotides of such a DNA sequence.
In a further aspect, the present invention provides a method for detecting M. tuberculosis infection in a patient comprising: (a) obtaining a biological sample from the patient; (b) contacting the sample with an oligonucleotide probe specific for a DNA sequence encoding the above polypeptides; and (c) detecting in the sample a DNA sequence that hybridizes to the oligonucleotide probe. In one embodiment, the oligonucleotide probe comprises at least about 15 contiguous nucleotides of such a DNA sequence.
In yet another aspect, methods are provided for detecting tuberculosis in a patient, such methods comprising contacting a biological sample with one or more polypeptides encoded by a DNA sequence selected from the group consisting of SEQ ID NO: 2-10, 102, 128, the complements of said sequences, and DNA sequences that hybridize to a sequence recited in SEQ ID NO: 2-10, 102, 128; and detecting in the sample the presence of antibodies that bind to the polypeptide, thereby detecting M. tuberculosis infection in the biological sample. Diagnostic kits for use in such methods are also provided.
In another aspect, the present invention provides antibodies, both polyclonal and monoclonal, that bind to the polypeptides described above, as well as methods for their use in the detection of M. tuberculosis infection.
These and other aspects of the present invention will become apparent upon reference to the following detailed description and attached drawings. All references disclosed herein are hereby incorporated by reference in their entirety as if each was incorporated individually.